How do you use math as an adult?

Miscellaneous and Personal Stuff I Must Share
61

The main reason to learn “higher” math (beyond arithmetic or simple fractions) is for “numeracy”, a sense of what is actually right, and a feeling for the right way to think about something if you want to get to the right answer.

But in terms of “high school math”, the #1 thing I use from that aside from work are from probability, counting, and combinatorics, as applied to playing games. And understanding of how compounding works (as with paying or receiving interest) is pretty important to understand why thinking in terms of “can I afford my monthly payment” is a debt trap lenders are eager to profit from.

In both cases it’s not usual that I have the time to sit down and “do the math” to come out to an exact answer in real time, but simply having done that exercise enough times that my “feel” for what’s going on is much better than most people’s naive understanding. A lot of people, when dealing with some kind of random choice, kind of just assume things are “about 50/50?” in odds.

What has also proven useful, again not necessarily sitting down and doing the math every time but just having internalized the concepts, is understanding the different kinds of means (averages) - specifically, harmonic mean vs. arithmetic mean (straight average). For example, a lot of people get speed (miles/hour) or fuel economy concepts wrong (miles/gallon) because they use the wrong denominator when computing an average to track or to compare things, because they’re not actually thinking about what the rates mean but are “just manipulating numbers like any other numbers” - following numerical recipes, which is “shallow math” and not “actual math”.

For example, if you drive to a point 25 miles away at a steady 50 MPH and then came back at 100 MPH, what was your average speed for the round trip?

No, it’s not (100+50)/2 = 75 MPH, even though the distance both ways is obviously the same, because the rate is “per hour” (in time), not “per mile” in distance. You drove 25 miles at 50 MPH, which means it took you 30 minutes; and then drove 25 miles back at 100 MPH, which took you 15 minutes. So you drove a total of 50 miles in 45 minutes, which is 50 miles / 45 minutes * 60 minutes per hour = 66.67 MPH. Which is what the “harmonic mean” computation would give you.

Now, if you’d driven 30 MINUTES at 50 MPH and then 30 MINUTES at 100 MPH, then your average speed would indeed be 75 MPH, the straight average. Because the denominator is now the same concept as the rate (the time not the distance).

You don’t have to remember how to do a harmonic mean off the top of your head (it’s a spreadsheet function for me), the important bit is to realize when you SHOULDN’T use a straight arithmetic average.

And the critical thing to learn in high school math is that if your answer was right, you can check it by plugging it back in. Was your average speed, in fact, 75 MPH? Computing the time you actually took to make the round trip immediately makes it obvious you’ve done the wrong thing. So if you aren’t sure if you’re making a “wrong average method” error, you can easily find out.

62

Latest use of math not related to my job: figuring out the best direction to place solar panels. Start with geometry of the earth’s orbit and rotation, then other things like panels shading each other. I used vectors, but I’m sure it’s doable with traditional geometry.

Quoted for emphasis. Working with numbers gives you a feel for numbers, which even if you don’t know the right answers, at least you’ll be asking the right questions.

63

I’m a forester.
When cruising timber I use trig to calculate tree heights. I use statistic because those trees are part of plots, and I need to calculate sample intensity, total volume and variability/error.
I use that data to do appraisals, which incorporate selling value by species minus costs, including stump to truck costs, hauling, profit and risk, road use fees, scaling etc.
I design logging roads, and calculate cut and fill, bridges and bridge abutments, slopes and turning radius.
I convert between slope distance and ground distance when laying out stream buffers.
I occasionally use coordinate geometry and can plot and find UTM and latitude and longitude coordinates.
I convert between map distance and ground distance.
I use just about everything I was ever taught.

My field is really STEM heavy, but that’s not what students entering my field think.

64

I’m a programmer, so word problems are basically what I do for a living. Someone tells me what they know and what they want to know, and it’s my job to figure out how to get from the beginning to the end. I let the computer do the math, but I have to figure out what math the computer will do

Also, I’ve used c=2πr to make circle skirts for myself.

Are you trying to give them new problems that you feel might be more relevant, or are you just trying to justify teaching math to them, or to yourself? Or just wondering if people actually use math?
To me, the real reason why math is needed is the same as why football players run through paths of tires. You never find tires on the playing field, but it builds muscles that help the players when they’re on the field. So you may never actually consciously use math (except, hopefully things like sanity checks on money transactions, etc.), but you’re using mental muscles built by your math lessons to do things better.

65

See this is the problem I have with how many talk about education in general these days. “I’m never going to use that” says the high school freshman who doesn’t have the slightest clue of what they will be doing in 10 years. I wanted to be an architect. Now I’m in charge of building, commanding and controlling satellites. I became more interested in building things rather than buildings, so I decided to be an engineer.
Different skill set. Similarly I know a lot of liberal arts majors who are now in IT. By stopping math at “checkbook balancing” which I learned in like sixth grade, or not teaching the sciences, history or art, you close a lot of doors to opportunities and potential interests that a student might not know about, but might find interest in once exposed.

66

They actually do have real world experience and questions. I suspect they could come up with all sorts of ideas and questions that require math. It’s hard to teach when you can’t write the lesson plan…my sympathies!

67

You don’t think of using a tape measure as maths until you have to teach multiple adults how to read one. Everyone will end up using one at some point.

68

I go to great lengths to not use one.

69

Major PITA. I had to do this for young electrician students in the Navy. It was painful watching one guy lying on the ground on his stomach, tape measure stretched out along a piece of conduit, while he laboriously ticked off 1/16" increments.

70

Leaving out my occupation in a STEM field, math is useful all the time.

Cooking. Car-related. Anything finance. Property ownership. Tax rates. Travel and leisure. Budgeting. Hobbies such as woodworking.

These all use arithmetic, algebra, trig, and even calculus. No, I’m not doing things like computing rates of change manually; but I know how to do so, and know why it works, and so have trust that I’m doing it correctly when plugging formulas into Excel.

71

My DIL does taxes, in the season. She’d make less if more people could do their own.

Although, sadly, a lot of people who pay to have simple taxes done are doing it to get ~90% of their refund now, rather than having to wait for it. As in, they’re paying a fee and 10% of their refund to get the rest now. I don’t think that’s a problem with math, exactly.

72

Really? I bombed algebra, and was a so-so geometry student. I knew how to use a tape measure before I was in school; I would take the one out of my dad’s junk drawer and measure things to my heart’s content. Whatever family member I asked told me what the marks meant. I didn’t have a good handle on fractions beyond a quarter until second grade or so, but using a tape measure ranks pretty high on the list of easiest things for me to learn.

73

Americans are in a special, unique position. We have to use math daily, to convert the weights and measures that are uniform in the rest of the world. I’ve found it very useful to know how to convert quickly in my head. Traveling, I do a lot of currency conversion, too.

It would never occur to me to reach for a phone to do math that 'i can do pretty well in my head.

74

Does any Doper use the Quadratic Equation for anything?

75

Do you mean a quadratic equation, or the Quadratic Formula? A quadratic equation is a particular type of algebraic equation, of which there are many specific examples. The Quadratic Formula is a formula that gives the solutions to any particular quadratic equation.

Both do come up in higher-level math and other STEM fields (e.g. problems involving projectile motion), but you asked for “other than working in STEM fields” in your OP. Offhand I can’t think of an application to non-STEM “everyday life,” but I would be interested in hearing what, if anything, other Dopers do use quadratic equations and/or the Quadratic Formula for.

Here’s one page I found of “real world examples of quadratic equations.” They may be the kind of thing you’re looking for, or you may find them too contrived or artificial or STEM-y.

76

I’m an Engineer, and use math on a daily basis. Sometimes simple algebra, sometimes a li’l calculus, sometimes generating or interpreting statistics.

I’m actually taking Calculus over again, as per-requisites for another Engineering degree.

Tripler
I just re-started Calc II.

77

Surveyor/mapper for work, programmer/computer nerd for fun.

I math a lot.

Rarely a day goes by that of course algebra of some sort isn’t being used. I use sines/cosines often for converting distances from angled measurements to cardinal distances for proportional calculation of missing monuments.

As a general rule, we work in decimal feet for measurements, but often engineers provide plans in architectural units (what we call using fractional inches) so I do a lot of conversions back and forth, as well as from metric to US Survey Feet.

I also do a lot of simple coordinate geometry, so Pythagoras is a hero to me.

78

When I lived in Chile I had none of my usual resources (no internet then) so I had to create my own star charts, using a table of star coordinates found in a dog-eared old World Almanac. And I had a view of the Pacific, so I worked out my own formula for determining the distance to the horizon based on height of the observer.

Those are few examples, but the point is, I could do it.

79

I met Paulos many years ago and have an autographed copy of the book. Shortly after reading it, I calculated the speed at which my fingernails grow in mph. (Much easier to do than hair. Trim your nails all the way down, wait a month, measure the length.)

I found it to be about 1/4 inch per month, or about 5.5 billionths of 1 mph (8.8 billionths of 1 kph).

Doing that exercise gave me a much clearer insight into just how big a billion is. A mile is a large (on the human scale) but fairly comprehensible unit of measure. If you asked most people to show you with their fingers how much a billionth of a mile is, I’ll bet a lot of them would hold thumb and forefinger maybe a half or a quarter of an inch apart. But that’s way too much for even a millionth of a mile, which is a tiny bit more than 1/16th of an inch. One billionth of a mile is 1/1000th of 1/16th of an inch.

And every hour, my fingernails grow 5.5/1000ths of 1/16th of an inch.

80

Oh boy howdy to I have questions for you!.

Tripler
We’ll have to share a cup of coffee some time.